Pope Benedict XVI's resignation came like a bolt from the blue overnight.

And the weather around the Vatican was eerily appropriate, with lightning striking St Peter's Basilica, one of the holiest Catholic sites, on the same day that Pope Benedict announced he would be stepping down.

Global news agency Agence France-Presse published an image of lightning striking the basilica's dome, which it said was taken "on the day the Pope" announced his resignation.

AFP said the striking image was captured by photographer Filippo Monteforte, who works for Italian national news and photo agency ANSA.

Monteforte's website shows that he has photographed the Pope extensively for for more than a decade. He is also listed as a AFP photographer, with a portfolio of his work on the news agency's website.

The image was doing the rounds on social media overnight, with some people questioning its authenticity.

Fairfax Media photographer Nick Moir said the image looked genuine.

"It's probably not that rare for St Peter's to get hit," he said. "The bolt is hitting a lightning rod to the side of the cross, it seems."

When Pope Benedict was elected at the age of 78 in 2005, he was an old man in a hurry. He knew that in the course of nature he did not have long. His priorities were not those of a politician, and, an academic by training, he set out to epitomise his thought in four encyclicals: on charity, hope, social justice and (still to come) faith.

He also succeeded in finishing a trilogy of books on the life of the central figure of Christianity, Jesus of Nazareth – written, surprisingly, in his private capacity, not as pope. But nothing surprised the world like his resignation.

To resign as pope seems a very modern step (even if the precedents were medieval) and the motive entirely reasonable: “incapacity to fulfil adequately the ministry entrusted” to him. Joseph Ratzinger’s reasonable outlook was exactly the impression he left when he visited Britain in 2010. The naysayers misjudged the public reaction.

In Westminster Hall, the Pope argued for “the legitimate role of religion in the public square”, and his audience of MPs and peers listened, and applauded, as did the nation beyond. This was not the mythical Rottweiler his enemies portrayed

The last pope to resign, Gregory XII, did so in 1415, 10 years into his tenure, in the midst of a leadership crisis in the church known as the Great Western Schism. Three rival popes had been selected by separate factions of the church, and a group of bishops called the Council of Constance was trying to heal the schism. Gregory XII offered to resign so that the council could choose a new pope whom all factions would recognize. It took two years after Gregory XII’s departure to elect his successor, Martin V.

Other popes known to have resigned:

Pope Celestine V: A recluse who only reluctantly accepted his election in 1294, Celestine V resigned and fled the Vatican after just three months to wander in the mountains. According to a history timeline on Christianity.com, the bishop who became his successor, Boniface VIII, was intent on ensuring that Celestine V did not become an example for future popes, and ordered Celestine V seized and imprisoned as he was about to sail to Greece. He died in custody in 1296 at the age of 81, and was declared a saint in 1313.

Benedict IX: One of the youngest popes, he was elected at the age of about 20 in 1032, and became notorious for licentious behavior and for selling the papacy to his godfather, Gregory VI, in 1045, and then twice reclaiming the position.

Gregory VI: Considered a man of great reputation, Gregory VI had thought Benedict IX unworthy of the papacy, and essentially bribed him to resign. He was recognized as pope in Benedict’s stead, but when Benedict’s attempt at marriage failed and he wanted to return to the papacy, a power struggle ensued. A council of bishops called upon Gregory VI to resign after less than two years in office because he had obtained the papacy through bribery.

Yes, a pope can resign -- up to 10 popes in history may have resigned, but historical evidence is limited. Most recently, during the Council of Constance in the 15th century, Pope Gregory XII resigned to bring about the end of the Western Schism and a new pope was elected in 1417. Pope Celestine V's resignation in 1294 is the most famous because Dante placed him in hell for it.

Most modern popes have felt resignation is unacceptable. As Paul VI said, paternity cannot be resigned. In addition, Paul feared setting a precedent that would encourage factions in the church to pressure future popes to resign for reasons other than health. Nevertheless, the code of canon law in 1917 provided for the resignation of a pope as do the regulations established by Paul VI in 1975 and John Paul II in 1996. However, a resignation induced through fear or fraud would be invalid. In addition, canonists argue that a person resigning from an office must be of sound mind (Canon 187).

In 1989 and in 1994, John Paul II secretly prepared letters offering the College of Cardinals his resignation in case of an incurable disease or other condition that would prevent him from fulfilling his ministry, according to Msgr. Sławomir Oder, postulator of the late pope's cause.

The 1989 letter was brief and to the point; it says that in the case of an incurable illness that prevents him from "sufficiently carrying out the functions of my apostolic ministry" or because of some other serious and prolonged impediment, "I renounce my sacred and canonical office, both as bishop of Rome as well as head of the holy Catholic Church."

In his 1994 letter the pope said he had spent years wondering whether a pope should resign at age 75, the normal retirement age for bishops. He also said that, two years earlier, when he thought he might have a malignant colon tumor, he thought God had already decided for him.

Then, he said, he decided to follow the example of Pope Paul VI who, in 1965, concluded that a pope "could not resign the apostolic mandate except in the presence of an incurable illness or an impediment that would prevent the exercise of the functions of the successor of Peter."

"Outside of these hypotheses, I feel a serious obligation of conscience to continue to fulfill the task to which Christ the Lord has called me as long as, in the mysterious plan of his providence, he desires," the letter said.

Pope Benedict XVI announced his resignation with grace and humility. He was heeding the call of conscience and recognizing his own human limitations.

While there have been resignations in the papacy’s past, letting go of papal power has never been framed in such a powerful way.

There is indeed power in letting go.

Letting go allows for the operation of the Holy Spirit, for it is by recognizing our own limitations we find, paradoxically, the power to transcend them. But there are also more worldly implications to the process of letting of go in this particular case. By giving up the papacy in this way, and at this time, Benedict will have the opportunity to shape the choice of his successor.

Benedict’s papacy has been marked by personal humility and a continuing reassertion of papal authority worldwide. Benedict did not include the pPapal tiara on his coat of arms, preferring instead a bishop’s mitre. He has also shown himself to be uncomfortable with the personal adulation that often accompanies the papal office. When he speaks, it is in measured cadences full of theological depth and complexity.

Pope Benedict's resignation has been planned for some time – Rowan Williams, the former archbishop of Canterbury, knew about it before Christmas – but it is still a stunning shock to the outside world. No pope has willingly resigned since Pope Celestine V in 1294. Pope John Paul II hung on for years – he was dying of Parkinson's disease – while the machinery of the Vatican rotted about him.

During the decrepitude of John Paul II, Pope Benedict, as Cardinal Ratzinger, was his right-hand man. It may be that his experience then planted in him a wish to leave office while he was still able to discharge his duties.

Although his accession was greeted with horror by the liberals in the church, he spent almost all his time in office struggling ineffectually with the problems inherited from John Paul II. His most remarkable innovation was his decision to resign as he felt his powers failing. That ought to be a precedent that the church will make use of again.

His most lasting legacy, I would suggest, will not be in the various “newsworthy” acts of his papacy that were highlighted in the media so often (his long negotiations with the breakaway Society of St. Pius X, his strong actions against the sexual abuse accusations made against the powerful founder of the Legion of Christ, the revised English translation of the Mass, his own response to the sexual abuse crisis, or the controversy over the comments that angered the Muslims, and so on) but something far more personal: his books on Jesus.

Far more people will most likely read those moving testaments to the person who is at the center of his life—Jesus of Nazareth—than may read all of his encyclicals combined. Others may disagree about this aspect of his pontificate, but in these books, the pope brought to bear decades of scholarship and prayer to the most important question that a Christian can ask: Who is Jesus?

This is the pope’s primary job--to introduce people to Jesus--and Pope Benedict did that exceedingly well.